The present invention relates to diaphragms for pressure sensors and the method of forming same.
Various configurations of diaphragms have been used in a wide variety of pressure sensor devices with the primary object of these diaphragms being to seal the inside of the device from the surrounding environment while allowing the force collector to move in response to the measured pressure. To this end, metal sheet-like elements generally of circular configuration have been used. The contour of such diaphragms is also generally symmetrical about a central axis with concentric, convex and concave deformations in the sheet. The deformations act to reduce the force required to bend the diaphragm in response to movement of the central force collecting piston of the pressure sensor. The deformations also are intended to relieve radial stress in the diaphragm as the force collecting piston moves axially under pressure load.
The resistance which is encountered with such diaphragms is generally non-linear. This is in part because the radial strain experienced by such diaphragms is related to the axial movement of the force collecting piston by the approximated relationship that the elongated radial width of the active portion of the diaphragm is equal to the square root of the sum of the squares of the relaxed radial width of the active portion of the diaphragm and the axial displacement of the force collecting piston. Such a non-linear relationship affecting the performance of the diaphragm results in a non-linear response of the sensor to pressure. Calibration of the instrument over its operating range.
Another difficulty encountered by thin metal diaphragms is stress concentration at both the annular mounting rim of the sensor and the force collecting piston. Diaphragm failure is frequently experienced at these points rather than at some intermediate point therebetween. The abrupt change from the flexible unsupported portion of the diaphragm to the rigid components of the sensor is primarily responsible for these problems.
In attempting to overcome the foregoing difficulties, i.e., a non-linear spring rate of the diaphragm and high stress loadings at the attachment points, various configurations have previously been employed. However, efforts at solving these problems have generally resulted in an improvement in diaphragm performance with respect to one consideration at the expense of the other consideration. Consequently, no real solution to the improvement of overall diaphragm performance has heretofore been found.